1. Field of the Invention
The present invention relates to coating compositions containing aliphatic polyisocyanate-aminosilane adducts and hydrolyzable silanes, and to substrates coated with these compositions.
2. Description of the Prior Art
The paint industry requires sophisticated coatings, e.g., in the automobile industry, which possess an ideal combination of very good mechanical properties, such as very high hardness and abrasion resistance, and also excellent flexibility and very good chemical properties, such as solvent and chemical resistance.
It is known that purely inorganic coating compositions based on a siloxanes, which have been produced by reacting hydrolyzable silane groups with water or dehydrating agents, are distinguished by high scratch resistance and chemical resistance. A generally known process for producing these purely inorganic coatings is the sol-gel Eprocess, which is described in detail by C.J. Brinker and W. Scherer in "Sol-gel science: The Physics and Chemistry of Sol-gel Processing", Academic Press, New York (1990). A severe disadvantage of these purely inorganic coatings is that they are brittle and prone to stress cracks. Therefore, purely inorganic coatings are not suitable for flexible substrates.
Various attempts are known from the literature for combining the positive properties of purely inorganic coatings with the properties of organic coatings. An overview of the so-called inorganic-organic hybrid coating compositions is found in J. Mater. Chem. 6 (1996) 511. Specific combinations are disclosed in U.S. Pat. No. 5,378,790, U.S. Pat. No. 5,344,712, U.S. Pat. No. 5,316,855, EP-A 565,044, EP-A 505,737 and in DE-A 4,020,316. However, none of these prior art coating compositions provides to the full extent the combination of properties required by the paint industry.
It is an object of the present invention to provide a coating composition that exhibits an improved balance between high hardness, abrasion resistance and chemical resistance on the one hand and high flexibility on the other.
Reaction products of aminosilanes with polyisocyanates are known (see e.g. "Adhesives Age", 5/1995, p. 30 ff.). Such moisture curing, alkoxy-silane-terminated polyurethanes are used increasingly in flexible sealing and adhesive materials curing at room temperature U.S. Pat. No. 5,700,868, U.S. Pat. No. 4,625,012, U.S. Pat. No. 4,474,933, U.S. Pat. No. 3,979,344, DE-A 4,234,325, DE-A 2,155,259). However, none of these literature references describe condensation products of aliphatic polyisocyanate-aminosilane adducts with hydrolyzable silanes and their use in sol-gel paints.
Surprisingly, it has now been found that condensation products of aliphatic polyisocvanate-aminosilane adducts with hydrolyzable silanes exhibit in sol-gel paint preparations an improved balance between high hardness, abrasion resistance and chemical resistance on the one hand and high flexibility on the other. The polyisocyanateaminosilane adducts react with the hydrolyzable silanes via polycondensation to form flexible inorganic-organic hybrid coatings having high hardness and very good solvent resistance.